1. Field of the Invention
The present invention is related to controller/drivers for driving display panels, and methods of operating the same, more particularly, to controller/drivers including a display memory for storing display data representative of images to be displayed.
2. Description of the Related Art
Portable devices, including cell phones and PDAs (personal data assistant), are usually composed of a liquid crystal display (LCD) for user interface. Such portable devices typically use a controller/driver for driving the LCD. Typical controller/drivers drive an LCD in response to bitmap data received from a CPU provided within the mobile portable.
As disclosed in Japanese Open Laid Patent Application No. Jp-A-Heisei 9-281950, controller/drivers often include display memories for storing display data. Such controller/drivers temporarily store display data in the display memories; display data stored in the display memories are used for driving LCDs.
One of the recent user's requirements for portable devices is highly sophisticated display on the LCDs. Many users of portable devices desire displaying fine images with highly intense grayscale, and moving pictures with improved smoothness on the LCDs. Therefore, recent portable devices often include a high resolution LCD and a controller/driver adapted to display high grayscale images and smooth moving pictures.
One of the problems in providing highly sophisticated display is that an increased amount of display data is required to be transmitted to controller/drivers. Improving fineness and grayscale resolution of images, and smoothness of moving images is inevitably accompanied by considerable increase in the amount of image data to be transmitted to controller/drivers. The increase in the image data transmitted to controller/drivers undesirably increases power consumption of the controller/drivers, because controller/drivers consume power for receiving data bits of image data. Increase in the power consumption is quite significant, especially for portable devices. Additionally, the increase in the image data transmitted to controller/drivers undesirably leads to increased EMI (Electromagnetic interference), because controller/drivers emit EMI when receiving data bits of image data.
The inventors have discovered that a controller/driver architecture in which images are partially transmitted by using a vector form, not by the bitmap form, is preferable for satisfying the users' requirements. From the inventors' recognitions, the bitmap form is suitable for representing some images displayed on portable devices, and vector forms are suitable for representing other images. Photograph images, which require many graylevels for achieving rich representations, such as fine gradation, are suitable for being represented in the bitmap form. On the other hand, images mainly represented by contrast, such as video game images and map images, are not suitable for the bitmap form, because the use of the bitmap form unnecessarily increases the data size. Additionally, representing moving pictures by image data in the bitmap form undesirably necessitates increased data transfer. The inventors consider that the bitmap form should be used for transferring images which require rich representations, such as photograph images, and another form, including a vector form, should be used for transferring images which require reduced data transfer, such as video game images and map images. This technique, which is not in the public domain to the inventors' knowledge, would be effective for reducing data transfer to controller/drivers with improved image qualities.
One of the issues for making this technique commercially available is size reduction of the circuitries incorporated within the controller/drivers. In general, data line drivers within controller/drivers are only adapted to bitmap images. Therefore, the use of a form other than the bitmap form necessitates incorporating a circuit converting the image data in the other form to the bitmap data into the controller/drivers; however, this undesirably increases the cost of the controller/drivers.
Therefore, there is a need for providing controller/drivers adapted to the bitmap form and another form with reduced circuit size.